1. Field of the Invention
This invention relates to a paper feed device used in a recording apparatus, and in particular to a paper feed device for automatically feeding cut sheets.
2. Related Background Art
Generally, a recording apparatus effects recording on sheets by a recording head, and a separate cut sheet feeder is used to feed the sheets continuously and automatically. However, this cut sheet feeder is provided discretely as an option and therefore, it leads to an increased cost when the apparatus is viewed totally. Thus, it is required to reduce the cost.
The sheets are not always fed in forward direction, but in some cases, they need to be fed in reverse direction. When the sheets are so fed in reverse direction, there arises a problem to be solved between the platen of the recording apparatus and the paper feed roller of the cut sheet feeder.
Also, the sheets need be reliably held during recording, and need to be positively discharged during the discharge thereof.
FIGS. 1A-1C of the accompanying drawings show an example of the feed device according to the prior art. In these figures, reference numeral 101 designates a paper holding pressure plate supported for pivotal movement about a pivot shaft 102 and keeping accumulated sheets of printing paper 103 biased toward a paper feed roller 104. The accumulated sheets of printing paper 103 have their leading ends kept drawable in the paper feeding direction of the arrow by a separating pawl 105, and clockwise rotation of the paper feed roller 104 can feed the uppermost one of the sheets of printing paper 103.
In such a feed device, the relative position of the pivot shaft 102 and the paper feed roller 104 is set so that the paper feeding direction is kept substantially horizontal when the thickness of the held sheets of printing paper 103 has become about one half of the maximum loadage as shown in FIG. 1B, and therefore, immediately after the sheets of printing paper 103 have been placed up to the maximum loadage as shown in FIG. 1A, the point F1 at which the sheets of printing paper 103 are pressed by the paper feed roller 104, as compared with the pressing point F2 in FIG. 1B, becomes rearward on the pressing surface 104A of the paper feed roller 104, and in the state of FIG. 1C in which the number of the remaining sheets of printing paper 103 has become small, the fore end of the pressure plate 101 becomes upwardly inclined and therefore, the pressing point F3, as compared with the aforementioned pressing point F2, becomes forward on the pressing surface 104a.
Moreover, the feeding direction of the printing paper 103 changes and therefore, the feeding state of the printing paper 103 immediately after being separated from the separating pawl 105 becomes unstable. Also, unless the pivot shaft 102 of the pressure plate is as much spaced apart as possible relative to the axis of the paper feed roller 104, the above-described tendency becomes remarkable, and the attempt to keep the distance therebetween great has led to a large shape of the pressure plate, which in turn has led to the disadvantage that the entire printer becomes bulky.
Also, from the viewpoint of space, the spacing between the feed roller and the paper feed roller cannot be made great, and this leads to a small degree of freedom of recording sheets and to a limited amount of reverse feed of the sheets.
So, use has been made of a feed device in which the feed roller is partly cut away in the circumferential direction thereof so that a large-diametered peripheral surface and a small-diametered peripheral surface are formed and paper feeding is effected by the large-diametered peripheral surface and as far as possible the sheet is not held long by the feed roller.
FIG. 2 of the accompanying drawings shows an example of such a feed roller. In this figure, reference numeral 200 designates a feed roller, and reference characters 200A and 200B denote the small-diametered portion and the large-diametered portion, respectively, of the feed roller 200. In this case, the feed roller 200 is rotated in the direction of arrow A, whereby sheets of printing paper 201 held on a base plate, not shown, are fed in the direction of arrow F2.
However, in the paper feeding operation by such a prior-art feed roller 200, the position at which the end edge of the large-diametered portion 200B of the feed roller 200 contacts the printing paper 201 deviates rearwardly relative to the axis 200C of the feed roller 200 and therefore, the operating direction F1 of the feed roller 200 for the printing paper 201 does not coincide with the feeding direction F2 and moreover, such a contact position P is displaced back and forth by the accumulated state of the sheets of printing paper 201, and this has led to a problem that the behavior of the printing paper 201 being fed becomes unstable.